Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine used to generate electrical power includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air may be supplied to the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more nozzles where the compressed working fluid mixes with fuel and ignites in a combustion chamber to generate combustion gases having a high temperature and pressure. The combustion gases flow through a transition piece to the turbine and expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
The combustion gases exiting the turbine include varying amounts of nitrogen oxides, carbon monoxide, unburned hydrocarbons, and other undesirable emissions, with the actual amount of each emission dependent on the combustor design and operating parameters. For example, a longer residence time of the fuel-air mixture in the combustion chamber generally increases the nitrogen oxide levels, while a shorter residence time of the fuel-air mixture in the combustion chamber generally increases the carbon monoxide and unburned hydrocarbon levels. Similarly, higher combustion gas temperatures associated with higher power operations generally increase the nitrogen oxide levels, while lower combustion gas temperatures associated with lower fuel-air mixtures and/or turndown operations generally increase the carbon monoxide and unburned hydrocarbon levels.
In a particular combustor design, one or more late lean injectors, passages, or tubes may be circumferentially arranged around the combustion chamber downstream from the fuel nozzles. A portion of the compressed working fluid exiting the compressor may be diverted to flow through the injectors to mix with fuel to produce a lean fuel-air mixture. The lean fuel-air mixture may then flow into the combustion chamber where it ignites to raise the combustion gas temperature and increase the thermodynamic efficiency of the combustor. Although the circumferentially arranged late lean injectors are effective at increasing combustion gas temperatures without producing a corresponding increase undesirable emissions, liquid fuel supplied to the late lean injectors often results in excessive coking in the fuel passages. In addition, the circumferential delivery of the lean fuel-air mixture into the combustion chamber may also result in liquid fuel streaming along the inside of the combustion chamber and transition piece, creating localized hot streaks that may reduce the low cycle fatigue limit for these components. As a result, a system for supplying liquid and/or gaseous fuel for late lean combustion without producing localized hot streaks along the inside of the combustion chamber and transition piece would be useful.